I'd still use a half-pound. There's no conversion factor; 25L isn't 2.5x sweeter than 10L. 25L will give a little bit more flavor, but for a half pound - it's close enough. The beer will be SLIGHTLY darker, but not enough where I would worry at all.
"I'm kind of toasted. But I looked at my watch and it's only 6:30 so I can't stop drinking yet." - Yooper's Bob "Brown eye finally recovered after the abuse it endured in Ptown last weekend, but it took almost a full week." - Paulie "no, he just doesn't speak 'stupid'. i, however, am fluent...." - motobrewer "... I'll go both ways." - Melana